In the processing of semiconductor devices, the substrate in which devices are fabricated undergoes a number of operations that are sequentially arranged to add to or subtract from the substrate layers or other features or to alter such layers or features. As the degree or scale of integration has increased in such devices, the need to preclude contaminants of all kinds has increased as well.
It is common to have multiple cleaning steps for every "productive" step. Thus, prior to each productive step the substrate will be cleaned to an ultraclean state. Associated with each cleaning step will be a number of cleaning operations which may include a hot acid cleaning, a hot base cleaning, a stripping operation or other wet or dry operation. Included with such associated cleaning steps will be a step to remove the cleaning agent and put the workpiece in a clean, dry condition for the next operation. Since entrained contamination can drastically alter the patterns produced, additively or subtractively, changing the integrity of the circuit, device, or the like, proper cleaning after photolithography and plasma etching is essential in order to achieve and maintain yields.
Particular problems in processing result from incompletely cleaned and/or dried workpieces. If organic materials are not completely removed; or if water spots, streaks or films are not dried and/or removed, the residues, hazes and/or organic films remaining on the workpiece may adversely interfere with the next level/layer of processing. Thus it is possible that the next layer of material to be applied will not properly adhere to the structure being formed, or the contaminants may otherwise interfere with subsequent processing to make further manufacturing steps ineffective, prohibitively expensive or no longer beneficial. Additionally, in building devices, it is noted that the structures become non-planar when patterns are formed in or on the substrate. These patterns can include grooves, trenches or holes as well as hills and valleys on the surface where particulate material and/or moisture may be trapped. Microparticles can lead to the creation of defects in the devices being fabricated, for example, causing shadows in a lithographic process or being metallized in a sputtering, evaporation or CVD process. In a similar manner, particulates may be trapped in a crevase in the structure and cause void formation or improper nucleation in some subsequent process steps.
U.S. Pat. Nos. 3,893,869 and 4,118,649 show cleaning apparatuses having an open cleaning tank which is adapted to have the cleaning fluid disposed therein energized by megasonic (ultrasonic) transducers. Megasonic energy is understood to be high energy ultrasonic energy in the frequency range from about 0.2 to 5 MHz. U.S. Pat. No. 4,543,730 provides a megasonic cleaning apparatus and a method for its use in cleaning semiconductor wafers and the like. This apparatus includes a buffer or intermediate closed tank to transfer (safely) the megasonic energy from transducers to an open cleaning tank in order to permit volatile, explosive cleaning fluids including alcohols to be used. No drying means are provided.
U.S. Pat. No. 4,854,337 is directed to a megasonic apparatus for cleaning semiconductor wafers arranged to accept the wafers to be cleaned in cassettes that dispose the wafers in a parallel vertical fashion and provides means to move the upwardly radiating megasonic transducers below and parallel to the surfaces of the wafers. The apparatus is open to the atmosphere.
Japanese Published Patent Application No. 59-202298 (English abstract) discloses the use of ultrasonic waves and organic cleaning solutions including alcohols for removing thermoplastic residued from molds.
Japanese Published Patent Application No. 60-92621 (English abstract) relates to a precision washing method that immerses workpieces in an organic solvent and thereafter sequentially treats them with alcohol, water, hydrogen peroxide solution, and ammonia solution, and then dries the workpieces by spinning or vacuum ethanol.
Soviet Union Patent Publication No. 983,913 (English abstract) is directed to improving the impregnation of electrical items by a cleaning process which entails preheating aromatic hydrocarbons, placing the items to be impregnated in such solution, reducing the pressure to vaporize the cleaning solution, increasing the pressure, and repeating the pressure reduction and pressure increase steps a number of times.
Workpieces have also been cleaned and dried in apparatus which include a spin dryer. Such apparatus does not produce streak free, particulate free workpieces because of uneven drying rates and redeposition of microparticles due to electrostatic forces.